Computer aided image analysis of biological material has become increasingly popular during the last years. For instance computer-aided processes for counting and classifying white blood cells in blood smears and body fluids have been developed. These types of analyses constitute an important step in diagnosing infections, allergies, or blood cancers.
In microscopic analyses of various medical preparations, for instance the analysis of a blood sample, a cytology sample, or a pathology sample, it is possible to use automatic scanning microscope systems. One example of such a microscope system is CellaVision DM 96 from CellaVision AB, which is used for localisation and pre-classification of the various types of white blood cells in peripheral blood smears. This system also pre-characterises parts of the red morphology and provides functionality for platelet estimation. The system scans a blood sample which is smeared onto a microscope slide. During scanning, the microscope system is making controlled positioning movements of the microscope slide in two directions, which can be referred to as directions in the x,y-plane. The microscope slide is placed on a table that moves in the two directions by means of two rails and a ball screw per direction.
A crucial part of such a system is to have a controlled handling of the sample. The sample, which is placed on a microscope slide, is to be transported from a cassette to the microscope where a coarse adjustment as well as a fine adjustment of focus is made to achieve a satisfying image of the blood sample. Several devices for loading slides from a cassette onto a stage of a microscope are known.
U.S. Pat. No. 6,847,481 discloses an automated slide loader cassette for a microscope. The automated slide loader comprises a slide cassette indexer for containing a plurality of microscope slides, a slide exchange arm for gripping a microscope slide within the indexer and for transporting the slide to a microscope for observation and then back to the indexer, and an x,y-stage for moving the slide exchange arm between the indexer and the microscope and positioning the slide for analysis.
There are problems associated with assuring that the two rails are perfectly parallel, and if they are not, the table will not be able to move properly.